The dimethyl terephthalate (which will be referred to as DMT hereinafter) is a main starting material for production of polyethylene terephthalate (which will be referred to PET hereinafter), which is a polycondensate product of DMT with ethylene glycol (which will be referred to as EG hereinafter). The Witten-Hercules method can be cited as a typical method for producing DMT.
The method of the present invention for producing the DMT comprises oxidizing p-xylene (which will be referred to PX hereinafter) and methyl p-toluylate with air, esterifing the resulting oxidized reaction mixture with methanol (which will be referred to MeOH hereinafter) under high-temperature high-pressure conditions, and collecting and refining the DMT from the esterifying reaction mixture.
However, there are problems that DMT produced from PX (which will be referred to PX-DMT hereinafter) according to the above method causes a hydrolytic reaction to occur when the PX-DMT is brought into contact with steam or the like, and acid components are formed as by-products, and, thus, the acid value of the resultant PX-DMT increases; and that the reaction product mixture contains a large amount of dimethyl hydroxyterephthalate (which will be referred to as HDT hereinafter) produced as a by-product by the oxidizing reaction, and thus the product exhibits a high intensity of fluorescence due to the presence of HDT, and the color of the product is bad.